Network Working Group A. Mishra
Internet-Draft O3b Networks
Intended status: Standards Track M. Jethanandani
Expires: May 25, 2018 November 21, 2017
BFD Performance Measurement
draft-am-bfd-performance-00
Abstract
This document describes an extension to the Bidirectional Forwarding
Detection (BFD) protocol to determine the optimal BFD transmit
interval for links with high one-way delay.
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [RFC2119].
Status of This Memo
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provisions of BCP 78 and BCP 79.
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This Internet-Draft will expire on May 25, 2018.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 2
3. BFD Performance TLV . . . . . . . . . . . . . . . . . . . . . 3
4. Theory of Operations . . . . . . . . . . . . . . . . . . . . 4
5. IANA Requirements . . . . . . . . . . . . . . . . . . . . . . 5
6. Security Consideration . . . . . . . . . . . . . . . . . . . 5
7. Normative References . . . . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Introduction
The Bidirectional Forwarding Detection (BFD) [RFC5880] protocol
operates by transmitting and receiving control frames, generally at
high frequency, over the datapath being monitored. In order to
prevent significant data loss due to a datapath failure, the
tolerance for lost or delayed frames in the Detection Time, as
defined in BFD [RFC5880] is set to the smallest feasible value.
This document proposes a mechanism to determine the smallest BFD
transmit interval that can be supported on the link. This is
achieved by actively measuing the one-way delay for each BFD session
and setting the BFD session intervals based on the measured delay.
This allows the BFD session to adapt to the fastest rate feasible on
the current active path.
2. Use Cases
To ensure stability, the BFD interval is typically set to value
greater than the one-way delay of the link. This value is currently
manually tuned based on the largest one-way delay in the set of links
over which the session can be established.
The method described in this proposal is useful in networks where the
network latency is high, or varies with time. Trans-oceanic links
and connectivity over geo-synchronous satellites are typical examples
of links where the latency is high and the difference in latency on
primary and backup paths can be significant.
Another use-case is connectivity using satellites in mid-earth orbit
(MEO) or low-earth orbit (LEO). In these systems the one-way delay,
while it is low (25msec to 150 msec), varies with time. This
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variation, based on various factors, can be as high as 30 msec. With
mobile receivers, such as ships, the delay when using such
connectivity can be non-trivial to predict. This requires an
automated method to determine the optimal BFD interval to allow
fastest possible recovery in case of failure.
Many networks employ the use of diverse link types for redundancy
where each link has significantly different link characteristics.
For example, using geo-stationary orbit (GEO) satellite backup for
MEO/LEO connectivity, or using fibre backup for MEO connectivity.
The end-to-end BFD sessions for services running on top of the
diverse transport will benefit from adaptive BFD rate.
3. BFD Performance TLV
The functionality proposed for BFD performance measurement is
achieved by proposing a new BFD Performance TLV to the BFD control
frame. This TLV leverages the delay measurement method defined in
RFC 6374 [RFC6374]. As BFD Version 1 control frame does not have
unused flags, the BFD Performance TLV overloads the BFD
Authentication Flag and uses a new auth type BFDP-AUTH-TYPE (code-
point TBA). The BFD Performance TLV merges the MPLS delay
measurement message with the BFD authentication TLV (while removing
fields that are not required for this application)
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Auth Type | Auth Len |Version| Flags | Control Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| QTF | RTF | RPTF | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp 1 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp 2 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp 3 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp 4 |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: BFD Performance TLV
where:
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Auth Type: The Authentication Type, which in this case is BFDP-AUTH-
TYPE (value to be assigned).
Auth Len: The length of the Authentication Section, in bytes.
Version: Currently set to 0.
Flags: As specified in Section 3.1 of RFC 6374 [RFC6374]. The T flag
is set to 1.
Control Code: As specified in Section 3.1 of RFC 6374 [RFC6374].
QTF: Querier Timestamp Format. The format of the timestamp values
written by the querier, as specified in Section 3.4 of RFC 6374
[RFC6374].
RTF: Responder Timestamp Format. The format of the timestamp values
written by the responder, as specified in Section 3.4 of RFC 6374
[RFC6374].
RPTF: Responder's Preferred Timestamp Format. The timestamp format
preferred by the responder, as specified in Section 3.4 of RFC 6374
[RFC6374].
Timestamp 1-4: Referring to Section 2.4 of RFC 6374 [RFC6374], when a
query is sent from A, Timestamp 1 is set to T1 and the other
timestamp fields are set to 0. When the query is received at B,
Timestamp 2 is set to T2. At this point, B copies Timestamp 1 to
Timestamp 3 and Timestamp 2 to Timestamp 4, and re-initializes
Timestamp 1 and Timestamp 2 to 0. When B transmits the response,
Timestamp 1 is set to T3. When the response is received at A,
Timestamp 2 is set to T4. The actual formats of the timestamp fields
written by A and B are indicated by the Querier Timestamp Format and
Responder Timestamp Format fields respectively.
The mapping of timestamps to the Timestamp 1-4 fields is designed to
ensure that transmit timestamps are always written at the same fixed
offset in the packet, and likewise for receive timestamps. This
property is important for hardware processing.
4. Theory of Operations
This delay measurement follows the method defined in Section 2.4 of
RFC 6374 [RFC6374].
The message is classified using the BFD authentication method defined
in RFC5880 [RFC5880].
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Method for determining the optimal BFD interval for a link with
certain delay charateristics is implementation specific and beyond
the scope of this document.
5. IANA Requirements
Requesting new BFD Authentication Type for BFD Performance TLV.
6. Security Consideration
Other than concerns raised in BFD [RFC5880], there are no new
concerns with this proposal.
7. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
.
Authors' Addresses
Ashesh Mishra
O3b Networks
Email: mishra.ashesh@gmail.com
Mahesh Jethanandani
Email: mjethanandani@gmail.com
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